The apparatus and system of the present invention have particular application in vehicle brake systems to convert the pivoting motion of a lever into an axial displacement of a brake piston and thereby produces a large force to actuate the brake shoes or brake jaws.
West German Offenlegungsschrift No. 3,103,398 shows a device comprising two opposing thrust washers having slanted confronting planar ramps. The thrust washers can turn with respect to one another and are maintained a predetermined distance apart by a plurality of balls. The angular rotation of one thrust washer relative to the other causes the balls to roll along the ramps which in turn produces a spreading movement of the washers which is a function of the angle of the ramps. This motion can then be transmitted to a brake piston for example.
In accordance with another prior known device relating generally to this field, European Patent Disclosure No. 190,453, cylindrical rollers are mounted between the confronting surfaces of two flat thrust washers having biased or slanted ramps. Relative rotation of the thrust washers causes the rollers to roll along the ramps and thus change the distance between the washers. One of the washers is supported in an axial direction so that it rotates inside a housing and the thrust washer is fixed against turning but is guided in such a way that it can move axially in the housing. A lever can be manipulated to turn the rotatable washer. Displacement of the second thrust washer is transmitted by a brake piston to the brake shoe of a disc brake. A relatively large axial force can be stored or built up in this way.
These prior systems have certain disadvantages and drawbacks. For example, it has been found that in these prior devices and systems, there is non-uniform loading of the rolling elements and this produces excessive local loading which ultimately can lead to premature failure of the system. This non-uniform loading is occasioned by production related differences in the height of the ramps, tolerance variables in the diameter of the rolling elements and the unavoidable eccentric introduction of the opposing force to the axially movable thrust washer. Furthermore, in systems utilizing cylindrical rollers, it has been observed that there is a considerable slip component in the region of the ends of the rollers. This produces high bearing friction and considerable wear in the components.